Tahajjud prayer is an optional night prayer in Islam. It can be performed after Isha prayer and before Fajr prayer. So the time period for Tahajjud prayer starts after performing Isha prayer and ends before the time for Fajr prayer begins. It is recommended to perform Tahajjud prayer in the last third part of the night, but it can be performed anytime between Isha and Fajr prayer. Therefore, the correct answer is "Isha' and Fajr".